Protesters are angry about rising food prices and the unstable economy.
Rights group say 40 people have been killed in anti-government protests, the government puts the figure at 19.
They are calling for President Omar al Bashir to step down.
But he remains defiant. He addressed his opposition group saying: "those who are seeking power, they are welcome. However, there's only one route to grab power - it is the ballot boxes. It is only through transparent, free elections."
But elections are more than a year away, and those protesting say they want him to step down sooner rather than later.
Al Jazeera's Hiba Morgan reports from Khartoum.